The orthogonal frequency division multiplexing (OFDM) technique provides crucial usage conveniences and benefits. OFDM has been preferred in several wireless communication technologies in the recent years. OFDM is a multi carrier waveform and it allows carriers to be practically brought together. It has been able to relatively meet high data rate and error performance expectations. However some characteristic problems of OFDM do not seem to be able to meet the new generation communication technique expectations.
Power consumption inefficiency due to especially peak-to-average power ratio problems and the disimprovement of data performances are important problems.
Moreover, the number of pilots that are used in order to protect data rates must also be limited.
Data rate losses can be observed in the multi input and output application and improvement of channel estimation of OFDM and additional improvement techniques are required due to its synchronization precision. Due to these reasons OFDM, brings about several problems together with it in real life. Even though OFDM supported with hierarchical modulation (HM) provides data rate increase, it still remains as a problematic technique due to its inefficiency relating to error performance loss and other problems.
In the OFDM technique that is enabled by HM, each subcarrier is formed to be modulated with HM. However due to its qualities and due to a critical problem it has only found use in a limited area. In this technique, only data rate increase is being targeted and an intermediate data rate between some known basic modulations is provided. The most important limiting factor is the interference effect that emerges due to low priority (LP) signals. Superposition coding (SC) function is present in the non orthogonal multiple access (NOMA) technique which can be provided as one of the last similar techniques. NOMA is a candidate technology that can be used in 5G and higher communication standards. This technique in which OFDM can also be used is not a waveform technique, but it is a multi access technique. Signals are formed according to the channel conditions of the receiver nodes and power distribution is adjusted accordingly. Together with this NOMA does not change the wave structure and therefore these are evaluated as different approaches and they can also be used together.
In the U.S. Pat. No. 7,558,191 numbered United States patent document of the known state of the art, methods of transmitting and receiving signals for wireless communication and especially wireless communication in OFDM networks are mentioned. The technique that has been given in the reference document resembles the hierarchical modulation technique. The high priority (HP) and LP symbols that are combined with SC are related to being sent to different users rather than the same user. In the document that has been given as reference it is aimed to reduce the interference effect between HP and LP symbols. Therefore, it does not comprise a waveform design such as a superposition coded orthogonal frequency division multiplexing system but it quite the equivalent of the HM technique.
In the article published in 2009 titled Implementation of OFDM-based Superposition Coding on USRP using GNU Radio, the physical layer application of an OFDM based superposition coding system in a software defined radio is described. This document is deemed to be similar to the NOMA technique. Moreover, as it is a technique that is prior to the NOMA technique, it can be counted as one of the studies that forms basis to NOMA studies. In the publication, multi-access technique has been targeted rather than a waveform and the signal to be received by multiple users is combined with the SC technique, similarly to the NOMA technique. Due to this reason, it is far from being in the same category with the superposition coded orthogonal frequency division multiplexing system.
As the loss of synchronization in communication systems leads to receiving a significant amount of erroneous signals, it also leads to reduction of user satisfaction, and decrease in spectral efficiency due to the need for re-transmission. Similarly, the ineffectivity of channel estimation also leads to these two results. The estimated error performance cannot be obtained in many cases due to some problems that have not been modelled in real time. This also causes expenses to increase and service quality to decrease. Moreover, especially under the light of new applications, the need for high data rates increases, however because of limited resources and channel conditions, the improvements of data rates are also limited.
The problem of PAPR is one of the most limiting factors that prevents communication quality improvement and due to this both power efficiency, error performance and communication quality are seriously degraded. In the MIMO systems that are of the most fundamental systems, PAPR problem and pilot contamination problems are also limiting factors and due to this, such systems cannot be realized.
The system subject to the invention not only provides solutions to these problems but it also has the potential to provide the energy efficiency in systems and cost advantages and management feasibility. Especially due to the significant solution mechanisms it has provided for MIMO systems, it has the potential to provide significant outcomes to development of high speed communication systems.